Fluorescent lighting technology has been in existence for over 50 years. Since its inception, what was gained in energy efficiency and decreased operating temperature, was lost in lighting quality and spectral purity. Historically, artificial lighting has evolved from light given off by fire, to light produced by incandescent bulbs, to fluorescent tubes, to the new "full-spectrum" fluorescent and incandescent bulbs. However, each lighting source has had its drawbacks. For instance, the incandescent bulb generates excessive heat and is high in energy consumption. Fluorescent light, on the other hand, gives off adequate light, is not excessively hot to the touch, but one of the drawbacks is that this light source emits far too much yellow and green spectral output, as compared with natural daylight. The "full-spectrum" bulbs currently available, come closer to producing the full spectrum of visible daylight, but these light sources utilize the red rare earth phosphors to emit the red spectrum of light which burn out in about one-half the life of the bulb, thus rendering their use prohibitively expensive. Thus, an inexpensive solution to the longstanding problem of inefficient, substandard lighting is sorely needed in today's lighting market.
The history of interior lighting design has generally focused on achieving lighting suitable to the task level, attractive in appearance, and energy efficient. In the past, however, the lighting designer did not factor certain aspects of the human vision system into the design of interior light sources. In particular, throughout the modern period of electric lighting, little consideration has been given to the "nonvisual" aspects of light.
Today, it is generally known that light is vital to human health and well-being. For example, it is known that light entering the human eye regulates body chemistry, especially the secretion or suppression of a biochemical substance known as melatonin. It is the melatonin levels in the blood stream that regulate human activity and energy levels. High melatonin levels causes drowsiness, while low melatonin in the blood stream corresponds to an alert state of human consciousness.
It is necessary to understand how the human body reacts to light before one can fully appreciate the benefits of artificial lighting capable of providing the full spectral output of natural daylight. Visible light is defined as electromagnetic radiation spanning the wavelengths of violet (380-430 nm), blue (430-490 nm), green (490-560 nm), yellow (560-590 nm), orange (590-630 nm), to red (630-700 nm). In terms of light having an effect on the human body, there are two physical pathways for light absorption: through the skin and through the eyes. It is also known that necessary photochemical reactions that occur within the body tend to involve very specific wavelengths of the visible light spectrum.
Today, the fluorescent tube, which produces a "cool-white" light has replaced the incandescent light in many interior lighting applications. Fluorescent light tubes arc very efficient forms of light as compared to incandescent lighting. For example, fluorescent light tubes can emit approximately four times as much light per unit of electricity as compared to a comparable incandescent bulb. However, even though fluorescent lamps provide a relatively high level of illumination, they fail to compensate for the necessary color-balance that natural light provides. It is now clear that there is a basic biophysical requirement for lighting that contains the proper levels of all seven constituent colors of the entire visible spectrum, that is, full spectrum lighting.
The benefits of full spectrum lighting are well-documented. An experimental study involving first grade classrooms equipped with either cool-white fluorescent lighting or full spectrum lighting showed that the children in the classroom that received full spectrum lighting were less hyperactive. In another group within the same study, the academic level of the learning disabled children rose substantially in the classroom with full spectrum lighting, as compared with that of the classroom with fluorescent lighting. Furthermore, with the same two groups, it was also found that the children exposed to full spectrum lighting had less cavities than their peers in the classrooms with cool-white lighting.
Additionally, full spectrum lighting has been shown to have an effect on ameliorating sleep disorders and increasing energy enhancement. It has been postulated that these positive effects of full spectrum lighting are due to the light's ability to regulate the body's melatonin and serotonin levels. Other positive effects have been seen with Seasonal Affective Disorders (SAD), which is triggered by the shortening of daylight in the winter periods. Again, the biochemical basis is thought to reside in the ability of full spectrum light to regulate melatonin levels.
Moreover, the effects of UV radiation emitted from fluorescent lighting has been addressed by several studies. Fluorescent lights work by placing an anode and a cathode at opposite ends of a glass tube. Inside a tube is a partial vacuum and a small amount of mercury vapor. When energized, the mercury vapor is ionized and emits ultraviolet (UV) radiation. The inside surface of the tube is coated with a phosphorous powder that "fluoresces" (gives off light) when stimulated by the UV radiation, and thus, visible light is produced. Not surprisingly, research studies have found that the incidence of malignant melanomas was considerably higher in office workers, as compared with individuals who were regularly exposed to daylight. Other recent studies have shown that the incidence of cutaneous malignant melanoma increases with exposure to normal fluorescent lighting. In this particular study, the data suggests that human exposure to fluorescent lighting may result in ultraviolet B dosages much greater than that of sun. Thus, there is also a need to filter or eliminate the UV radiation, especially the ultraviolet B component, that is emitted from fluorescent lighting.
There are still other problems inherent in the human use of fluorescent light sources. One particular problem is that fluorescent light tubes emit a high greenyellow spectrum of light. It is also known that the retina of the human eye is more sensitive to this particular portion of the visible light spectrum, that is, the cones or daytime receptors cells of the retina are activated in such a way as to result in a color shift, or unnatural color rendering, to the human eye. Thus, fluorescent lighting produces poor color rendering ability to the human visual system.
Additionally, the list of work and home-related complaints associated with the use and prolonged exposure to fluorescent lighting includes headaches, eyestrain, reduced attention span, reduced shelf life of meat and dairy products, yellowing of printed materials, and fading of dyed materials. Moreover, the health-related symptoms associated with the prolonged use of fluorescent lighting often result in absenteeism from work and substandard effectiveness on the job.
In U.S. Pat. No. 5,075,823 to Chomyn, an attempt was made to correct the green-magenta balance of the spectral output of fluorescent lighting utilizing a sheet of filter material positioned between a fluorescent bulb and a conventional lens or panel in a light fixture. This technique merely reduced some of the green portion of the visible light spectrum. The Chomyn patent nowhere describes a "full spectrum" attempt, nor anything else, except to achieve the "green-magenta" balance found in sunlight. In U.S. Pat. No. 3,112,886 to Kushner, an attempt was made to simulate the full spectrum of natural daylight by utilizing a coating of small colored beads or particles glued to a reflector or lens adjacent a fluorescent bulb. The mixture of particles disclosed in the patent is disproportionate with the proper correction of the spectral emissivity curves of both warm white and cool-white lighting. Thus, in both of these patents, full spectrum, or its close approximation was either not attempted or not achieved. Moreover, no previous attempts are known to have been made to correct, or eliminate, the harmful UV radiation emitted along with fluorescent light sources.
Thus, there is an urgent need to provide lighting sources that more closely resemble the spectral output of natural daylight, and at the same time reduce any harmful UV radiation, especially the ultraviolet B component, that is emitted as a consequence of the fluorescent lighting technology.